Background: Synthesis of metal oxides nanoparticles with specific morphology and size has become the subject of many experimental protocols. Biosynthesis of the nanoparticles using plants is more preferable than physical and chemical methods because of its environmental friendliness. Objective: The purpose of this study was to report the potential for green synthesis of cerium oxide nanoparticles using plant extracts with a high content of phenolic metabolites. Methods: We have synthesized the CeO2 nano- and microparticles using Petroselinum crispum aqueous extract. The particles were characterized by UV-visible spectroscopy, IR spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM) and dynamic light scattering analysis. For detection the reduction capacity of the extract the evaluation of total phenolic and flavonoid content as well as high-performance liquid chromatography-mass spectrometry (HPLC-MS) were performed. Biological activity of the particles was identified by bioluminescent tests and bio tests with Triticum vulgare. Results: Testing on T. vulgare showed that biogenic cerium dioxide powders stimulated the growth of up to 5-11,4% relative to intact samples, significantly increased the length of the leaves of seedlings and the root length. When seedings were exposed to the biosynthesized CeO2 particles, the level of chlorophylls was more stable and even slightly higher than control. Noticeable protective properties of the biosynthesized CeO2 powder under oxidation conditions were observed on the plant T. vulgare after a brief exposure (from 4 to 24 h). Conclusion: Thus, biogenic CeO2 can be potentially utilized in oxidative damage protection of agricultural plants.